This invention relates to a method and means for measuring distance of a moving object from a fixed point of reference.
Various attempts have been made to determine the distance of a moving object from a point of reference, utilizing the principle that when light emanates from a point source, the illuminance of a surface on which the light is shown varies inversely with the square of the distance from the source. When the surface is perpendicular to the light beam, this relationship can be defined by the following equation: EQU E=I/s.sup.2
Where "E" is the illuminance at the receiving surface, "I" is the luminous intensity of the light source, and "s" is the distance between the light source and the surface receiving the light. If the light source has a constant light intensity, then "I" becomes a constant, and the above equation produces an exponential curve when "E" and "s" are variable.
One prior art patent, U.S. Pat. No. 4,207,430, shows an attempt to sense the distance of a moving object by placing a light source on the moving object, and by receiving the light at a fixed point. In this prior art reference, the light source is placed upon the diaphragm of the speaker, and the receiver for the light source is placed at a fixed point of reference on the speaker.
A problem recognized by the inventor in U.S. Pat. No. 4,207,430 is the difficulty in utilizing a signal which behaves in a nonlinear fashion. Accordingly, the invention disclosed in U.S. Pat. No. 4,207,430 utilizes an optical guide means between the light source and the light receiver. The optical guide means causes the light intensity to vary with respect to the distance in a linear fashion, rather than in the normal exponential fashion, which would result if no obstructions were placed between the light source and the light detector.
One disadvantage of this prior art device is that it can maintain linearity in only a limited range of movement of the diaphragm. The linearity is only present in a range of a few millimeters (approximately 0.4 inch) whereas many speakers move a distance as great as one inch or more. The prior art device does not maintain linearity throughout this greater range of movement.
Therefore, a primary object of the present invention is the provision of an improved method and means for measuring distance of a moving object from a fixed point of reference.
A further object of the present invention is the provision of an improved method and means for measuring distance of a moving object which does not require an optical guide means or other light obstruction between the light source and the detector of the light source.
A further object of the present invention is the provision of an improved method and means for measuring the distance of a moving object, wherein an electrical detector circuit and an electrical linearization circuit are utilized for converting the light signal received from the moving object into a substantially linear electrical signal.
A further object of the present invention is the provision of a device which produces a feedback signal which remains substantially linear throughout an increased range of movement of the moving object.
A further object of the present invention is the provision of an improved method and means for measuring distance of a moving object from a fixed point of reference, which can be used in numerous applications, including the feedback systems for electrical speaker systems as well as other applications.
A further object of the present invention is the provision of an improved method and means which are economical to manufacture, durable to use, and efficient in operation.